Sms transport resource control

ABSTRACT

The invention provides for a method of controlling release of SMS transport resources between User Equipment and a MME of a communications network, wherein the release is permitted subsequent to a Control Protocol Acknowledge signal at a Mobile Switching Centre of the network, and in particular a method wherein the release is initiated by the MME responsive to receipt of a release signal, and further provides for a SGs Interface, and MME arranged to be employed with such a control method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 13/147,143 filedJul. 29, 2011, which is a National Stage of PCT/JP2010/050995, filedJan. 20, 2010 which claims priority based on GB Application No.0901539.7, filed Jan. 30, 2009, the contents of all of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to the control of Short Message Service(SMS) transport resources within a communications network and, inparticular, an Evolved Packet System (EPS) arranged withCircuit-Switched (CS) capable terminals.

BACKGROUND ART

In order to facilitate voice communication within Long Term Evolution(LTE) networks, various proposals have been forthcoming of which onecomprises so-called CS fallback in which a LTE User Equipment (UE) isarranged to “fallback” to, for example, GSM or UMTS, for thereceipt/transmission of incoming/outgoing voice communication.

CS fallback within EPS is primarily realised by using the SGs interfacemechanism provided between a Mobile Switching Centre (MSC)server/Visitor Location Register (VLR) or a Mobile Switching Centre(MSC)/Visitor Location Register (VLR) and the Mobility Management Entity(MME).

The SGs interface functionality is derived from the mechanisms specifiedfor the Gs interface in accordance with 3GPP TS 23.060.

Further, from 3GPP TS 23.272 there is provided an arrangement fortransporting SMS messages between a UE operating within a E-UTRAN(Evolved UMTS Terrestrial Radio Access Network) and the MSC within a CSdomain, by way of the SGs interface between the MME and the MSC/VLR forUEs attached to both EPS services and non-EPS services (CS services).

CITATION LIST Non Patent Literature

NPL Document 1: 3GPP TS 23.060

NPL Document 2: 3GPP TS 23.272

NPL Document 3: 3GPP TS 24.011

DISCLOSURE OF THE INVENTION Problem(s) to be Solved by the Invention

However, this known proposal is disadvantageously limiting in relationto the ongoing management of resources between the MME and UE whenarranged for SMS transport between the UE and the MSC/VLR. Although,from the stage 2 in step 10 in FIG. 8.2.2.1 of 3GPP TS 23.272 it issuggested that the MME may release the resources associated with the SMStransfer there is no indication whatsoever as regards the nature and/ortiming of any such release.

Control of the SMS resources therefore remains a limiting factorpreventing efficient deployment and, as required, release of suchservices.

The present invention seeks to provide for a method of controllingrelease of SMS transport resources, and also a related MME and SGsinterface offering advantages over known such methods and devices.

Means to Solve the Problem(s)

According to one aspect of the present invention there is provided amethod of controlling release of SMS transport resources between UserEquipment and a Mobility Management Entity (MME) of a communicationsnetwork, wherein the said release is permitted subsequent to a ControlProtocol Acknowledge signal at a Mobile Switching Centre of the saidnetwork.

The method is particularly advantageous in that it can be readilyidentified when the signaling connection between the UE and the MME isnot use any more.

Preferably, the said release can be permitted subsequent to receipt of aControl Protocol Acknowledge signal at the Mobile Switching Centre.

Further, the said release may be permitted subsequent to despatch of aControl Protocol Acknowledge signal from the Mobile Switching Centre.

Advantageously, the MME can be arranged to release the said resources.In particular, the MME can release the said resources responsive toreceipt of a release request signal.

According to another aspect of the present invention there is provided amethod of controlling release of SMS transport resources between a UserEquipment and a MME of a communications network, wherein the saidrelease is initiated by the MME responsive to receipt of a releaserequest signal.

The release request signal can be delivered from the Mobile SwitchingCentre.

Further, the release request signal can be introduced into the GsInterface of the network.

Of course it should be appreciated that the method can be providedwithin an Evolved Packet System network. The User Equipment can thencomprise a Circuit-Switched capable device such as a CS-fallback capabledevice.

Of course, the said release can be permitted subsequent to a ControlProtocol Acknowledge signal at a MSC/VLR.

According to a further aspect of the present invention there is provideda MME of a communications network including User Equipment and arrangedwith SMS transport resources there between, the MME further beingarranged to control release of the said resources.

As will be appreciated, the MME can be arranged to release the saidresources responsive to receipt of a release request signal.

Preferably the MME is arranged to release the said resources responsiveto a release request signal received from a Mobile Switching Centrewithin the network, although the actual timing of this will depend uponother traffic is present on the signaling connection between the UE andthe MME.

As noted above the MME can be provided within an Evolved Packet Systemnetwork, and also for communication with a Circuit-Switched capable UserEquipment such as CS-fallback capable UE.

According to yet a further aspect of the present invention there isprovided an SGs interface arranged to be provided between a MME and aMobile Switching Centre of a communications network, and arranged fordelivering a release request signal to the MME for control at the MME ofthe release of SMS transport resources between the MME and a UserEquipment of the network.

Advantageously, the release request signal originates from a MobileSwitching Centre of the network in the CS domain.

The interface can further be arranged to be provided within an EvolvedPacket System network.

A further interface can be arranged for use within a network employing aCircuit-Switched capable User Equipment as noted above.

EFFECT(S) OF THE INVENTION

Thus, it should be appreciated that the present invention can bearranged readily to cater for error, or abnormal, situations which mightoccur for example in the MSC. A maximum number of re-transmissionattempts for a Control Protocol Acknowledge signal can be provided forand, in combination with a timer function, should the that number bereached and/or the timer expire, the MSC can be prompted to requestrelease of the connection also in such error/abnormal conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described further hereinafter, by way of example only,with reference to the accompanying drawings in which:

FIG. 1 is a block diagram of an EPS architecture employing an MME and SGinterface according to an embodiment of the present invention;

FIG. 2 is a timing diagram for Mobile Originating SMS in idle mode andaccording to one aspect of the present invention;

FIG. 3 is a timing diagram relating to a Mobile Terminating SMS in idlemode and according to an aspect of the present invention; and

FIG. 4 is a timing diagram illustrating a relationship between anembodiment of the present invention and known proposals for GPRS MobileTerminating Messaging.

BEST MODE FOR CARRYING OUT THE INVENTION

Turning first to FIG. 1, there is provided a block diagram illustratinga network 10 employing an EPS architecture and illustratingcommunication between a UE 12 such as a cellular phone handset, and aMSC server 14. The architecture is arranged for CS fallback so as toallow for the incorporation of voice data onto the LTE system of the EPSarchitecture and various network possibilities for the UE 12 areillustrated such as UTRAN (UMTS Terrestrial Radio Access Network) 16,GERAN (GSM EDGE Radio Access Network) 18 and E-UTRAN 20. While the UTRAN16 and GERAN 18 can connect to the MSC server 14 by way of a ServingGPRS (General packet radio service) support Node 22, the E-UTRAN 20connects to the MSC server 14 by way of a MME 24 and by way of the SGsinterface mechanism 26 provided between the MSC server/VLR and the MME.

As is discussed further, the MME 24 embodying the present invention isarranged to provide control of the release of SMS transport resourcesand is arranged to receive a resource-release initiating message fromthe MSC server 14 by way of the SGs interface mechanism 26 which itselfalso comprises novel functionality in accordance with the presentinvention.

The arrangement provided within FIG. 1, and in accordance with anembodiment of the present invention, therefore provides a mechanism forthe release of SMS transport resources between the MME 24 and the UE 12and which is advantageously initiated only once a signaling exchangebetween the UE and the MSC/VLR has been completed and is described infurther detail below.

It is proposed that the MME receives a clear request from the MSC/VLRwhen the signaling exchange between the UE and the MSC/VLR is complete.In this way, the MME can identify with certainty that the signalingconnection between the UE and the MME is not used nor required anymoreby the MSC/VLR and such that the MME has full control of the Non-AccessStratum (NAS) signaling connection.

As will be appreciated from the following description, various messages,whether release request, release or error indication messages, arise onthe SGs and they can be arranged to contain an identifier of the UErelated to such messages. The identifier can be the IMSI (InternationalMobile Subscriber Identity) and this will allow the MME to know whichsignaling connection to release when receiving for example the releaserequest message. Likewise if an error or problem has arisen, it willallow the MSC to know for which UE there is a problem.

Discussed below with reference to FIG. 2 is the sequence for MO SMS(Mobile-Originated Short Message Service) in EPS. It is based on FIG.8.2.2.1 from TS 23.272 although the SMS PDUs (Protocol Data Units) havebeen added, and the sequence has been extended to cover the fullexchange of SMS PDUs.

Advantageously, the MME waits for the final SMS PDU (CP ACK) from the UEin order to transfer it to the MSC/VLR. The resources for the MO SMS arethen only released after the CP-ACK message has been received. However,it is appreciated that the MME cannot identify the contents of the SMSmessage, so the trigger for the SMS release therefore derives from theMSC/VLR, which advantageously knows whether the SMS transfer iscomplete. In the illustrated embodiment it is proposed to introduce suchrelease via the SGs interface noted.

With reference therefore to FIG. 2, there is illustrated a diagram ofsignaling arising between a UE 28, the MME 30, MSC/VLR 32, Home LocationRegister (HLR)/Home Subscriber Server (HSS) 34, SMS—Interworking MSC 36and Service Centre 38.

As will be appreciated, the signaling arises in relation to a CSfallback attach procedure 40 between the UE 28 and MME 30, MSC/VLR 32and the HLR/HSS 34 and commences with a UE triggered service request 42which leads to an uplink Non-Access Stratum (NAS) transport signal 44comprising Control Protocol Data and Relay Protocol Data elements.

Uplink unitdata messaging 46 including CP data includes RP data is thendelivered from the MME 30 to the MSC/VLR 32 via the SGs interface andthe MSC/VLR 32 initiates the forwarding of a short message 48 to theSMS-IWMSC 36 and onward message transfer 50 to the SC 38.

Subsequent to receipt of the uplink unitdata 46, the MSC/VLR 32 isarranged to return a downlink unitdata signal 52 including a CPacknowledge element to the MME 30 via the SGs interface and the MME 30in turn, provides a downlink NAS transport signal 54 to the UE 28 whichlikewise includes a CP acknowledge element.

Back at the SC 38, and subsequent to the receipt of the message transfer50, a delivery report 56 is returned to the SMS IW MSC 36 whichinitiates a onward delivery report 58 to the MSC/VLR 32 and the MSC/VLR32 then delivers a downlink unitdata signal 60 including CP data whichincludes RP acknowledge elements to the MME 30 via the SGs interface soas to initiate a further downlink NAS transport signal 62 which, thistime, includes CP data which includes RP acknowledge elements.

Importantly, and in accordance with the present invention, at this stagethe MME does not yet release the resources associated for the SMStransfer as noted above.

An uplink NAS transport signal 64 including a CP acknowledge element isthen delivered from the UE 28 to the MME 30 which, initiates an uplinkunitdata signal 66 from the MME 30 to the MSC/VLR 32 likewise includinga CP acknowledge element.

Receipt of this CP acknowledge element at the MSC/VLR 32 initiates anall important release request signal 68 delivered from the MSC/VLR 32 tothe MME 30.

The release request signal 68 provides a confirmed indication to the MME30 that the resources are not required anymore for the MSC such that theMME 30 can then release the resources whenever most appropriate anddepending upon other conditions specific to EPS traffic.

With regard to the details of FIG. 2, it should be appreciated that anembodiment of the invention can allow for control signaling in anopposite direction (i.e. from the MME to the MSC).

For example, if the NAS signaling connection between the UE 28 and theMME 30 becomes lost, the MSC/VLR 32 can be informed by way of a “releaseindication” message. The MSC/VLR 32 can then take appropriate actionssuch as suggested in TS 24.011 subclause 5.3.4 for example. Also an“error” indication could be usefully sent from the MME 30 to the MSC/VLR32 in situations of non-delivery of the SMS message by the MME 30 to theUE 28. Then the SMC entity in the MSC can take appropriate actions suchas suggested in TS 24.011 subclause 5.3.4 for example.

It should be appreciated that in these further instances, thefailure/error prevents the signaling after Downlink NAS Transport 62illustrated in FIG. 2 from arising.

Turning now to FIG. 3, there is provided a signaling diagram relating toa Mobile Terminating SMS in idle mode.

Again the resources for the MT SMS are to be only released after theCP-ACK message has been sent by the MSC/VLR and as before the MME willnot know the contents of the SMS message, so the trigger for the SMSrelease is derived from the MSC/VLR again, which is the only entityknowing whether the SMS transfer is complete. The release request fromthe MSC/VLR to the MME applies in relation to the signaling therefore ofFIG. 3 as it did for FIG. 2.

If incorporating this at this stage is not feasible, then I suggest weproceed with current proposal only, considering the short timescale.

Turning therefore in greater detail to FIG. 3, there is illustratedsignaling arising in relation to a UE 70, eNode B 72, MME 74, MSC/VLR76, HLR/HSS 78, SMS-GMSC 80 and SC 82.

The signaling illustrated again arises in relation to a CS fallbackattach procedure 84 for the UE 70, eNode B 72, MME 74, MSC/VLR 76 andHLR/HSS 78 and, since this illustration relates to a Mobile TerminatingProcedure, the signaling commences with a message transfer signal 86from the SC 82 to the SMS-GMSC 80 which then initiates a routineexchange messaging 88 with the HLR/HSS 78. Subsequently, signaling 90sending the short message from the SMS-GMSC 80 to the MSC/VLR 76 whichinitiates a series of paging signals 92, 94, 96 to the MME 74, eNode B72 and UE 70 in turn as illustrated.

A service request procedure 98 then commences with a service requestsignal 100 delivered from the MME 74 to the MSC/VLR 76 which returns adownlink unitdata signal 102 including CP data which includes RP dataelements via the SGs interface.

Upon receipt of the downlink unitdata signal 102, the MME 74 delivers adownlink NAS transport signal 104 including CP data which includes RPdata elements to the UE 70 which, in turn, sends an uplink NAS transportsignal 106 including CP acknowledge elements to the MME 74 and whichinitiates uplink unitdata signal 108, likewise including CP acknowledgeelements to the MSC/VLR 76.

Then, the UE 70 also delivers uplink NAS transport signaling 110including CP data and RP acknowledge elements to the MME 74 which inturn, delivers uplink unitdata including such CP data and RP acknowledgeelements 112 to the MSC/VLR 76 via the SGs interface.

In turn, the MSC/VLR 76 sends a downlink unitdata signal 114 including aCP acknowledge element to the MME 74 via the SGs interface.

Importantly, release of the SMS resources again does not occur at thistime but rather, in accordance with the invention, only subsequent to aspecific release request signal delivered from the MSC/VLR 76 to the MME74.

Upon receipt of the downlink unitdata signal 114, the MME 74 delivers adownlink NAS transport signal 116 to the UE 70 and which includes the CPacknowledge element. Subsequently, the MSC/VLR 76 sends a deliveryreport 118 to the SMS-GMSC 80 which, in turn, forwards on a deliveryreport signal 120 to the SC 82.

Only at this stage does the MSC/VLR 76 deliver a release request signal122 to the MME 74 so as to initiate release of the SMS resources by theMME 74.

Upon receipt of the release request signal 122, the MME 74 can readilyidentify that the resources are not required anymore for the MSC 76 suchthat they can be released at any appropriate time depending upon otherconditions specific to the EPS traffic.

Considering now possible interaction with SMS when concatenationapplies, for MO SMS, the UE 70 will not send final CP-ACK until thereare SMS transactions ongoing. So the end of SMS transfer for SMSconcatenation remains the CP-ACK received in the MSC/VLR 76 from the UE70. However, for MT SMS, the MSC/VLR 76 is responsible for the resourcesand can send the release request to the MME 74 at any time, when itknows that all SMS transactions are complete.

For a scenario involving simultaneous MO and MT SMS, the MSC/VLR isaware of all ongoing transactions and can send the release request tothe MME when all SMS transfers are complete. The MSC/VLR can then decidewhen to send the release request.

For abnormal cases or error cases at the MSC/VLR side it is alsoproposed to use such a release request.

In summary, the invention proposes to introduce a release request on SGsinterface for the MSC/VLR to indicate to the MME that the SMStransaction is complete. FIG. 4 is provided to illustrate this furtherand comprises an excerpt from 3GPP TS 24.011 for GPRS Mobile TerminatedMessaging on CM-sublayer in Iu mode and between a mobile station side124 and a network side 126. Importantly, the last step indicates aPMMSMS-REL-Req message 128 from the CM layer to the GMM layer in SGSNand the illustrated embodiment of the invention is based on an adaptionof this to the interface between the MSC/VLR and the MME.

It should of course be appreciated that the invention is not restrictedto the full details of the foregoing embodiment. For example, thecontrol of the release procedure need not be provided only in relationto a CS fallback system, nor indeed to an EPS system. Also, the releaseindication could be used also in relation to signaling in addition tothat for SMS between the MSC and the UE via the SGs interface.

Further, although the embodiments illustrated in FIGS. 2 and 3 relate toSMS transfer with the UE initially in idle mode, it should beappreciated that the invention can be readily employed in relation to UEin connected mode.

This application is based upon and claims the benefit of priority fromUnited Kingdom patent application No. 0901539.7, filed on Jan. 30, 2009,the disclosure of which is incorporated herein in its entirety byreference.

1. A method, performed in a visitor location register (VLR) as part of arelease procedure for a Mobile Terminating (MT) communication in acommunications network, the method comprising: the VLR sending an SGsRelease Request message after sending a CP-ACK message when an SMStransaction is complete.
 2. A method, performed in a Mobility ManagementEntity (MME) as part of a release procedure for a Mobile Terminating(MT) communication in a communications network, the method comprising:the MME receiving an SGs Release Request message from a visitor locationregister (VLR) after receiving a CP-ACK message when an SMS transactionis complete.
 3. A visitor location register (VLR) for performing part ofan SMS transport release procedure, for a Mobile Terminating (MT)communication, in a communications network, the VLR comprising: atransmitter arranged to send an SGs Release Request message to aMobility Management Entity (MME) after sending a CP-ACK message when anSMS transaction is complete.
 4. A Mobility Management Entity (MME) forperforming part of an SMS transport release procedure, for a MobileTerminating (MT) communication, the MME comprising: a receiver arrangedto receive an SGs Release Request message from a visitor locationregister (VLR) after receipt of a CP-ACK message when an SMS transactionis complete.